In general practise, a metal rich pregnant pulp or solution is fed into a cell of the above type which contains carbon, resin or like adsorbtion particles and where, by one means or another the adsorbtion particles become loaded with the metal values in the pulp. The adsorbent particles are then screen separated from the now leaner pulp which is then either pumped or gravity fed to an adjacent cell in a series of cells where the process is again repeated. Periodically, in order to achieve counter current movement of the adsorbent particles and pulp a quantity of pulp in any one tank is pumped together with its associated adsorbent upstream to the preceding tank. This arrangement causes back mixing which reduces the efficiency of counter current contacting. Gravity feed requires that sequential cells in the series be expensively vertically staggered in cascade and pumping involves the not inconsiderable expense of providing and maintaining the pumps and motors required to do this. Often air or oxygen is required in the leaching process and this is generally supplied by means of a blower, compressor or from a pressurised vessel which feeds the air or oxygen to the tank where it is then diffused in one way or another below the surface of the pulp in the tank. Again the provision of compressed air or oxygen and diffusers is expensive.